Chiral or achiral, mesoporous carbon

ABSTRACT

A composition and a method for producing mesoporous carbon materials with a chiral or achiral organization. In the method, a polymerizable inorganic monomer is reacted in the presence of nanocrystalline cellulose to give a material of inorganic solid with cellulose nanocrystallites organized in a chiral nematic organization. The cellulose can be carbonized through thermal treatment under inert atmosphere (e.g., nitrogen or argon) and the silica may subsequently be removed using aqueous solutions of sodium hydroxide (NaOH) or hydrogen fluoride (HF) to give the stable mesoporous carbon materials that retain the chiral nematic structure of the cellulose. These materials may be obtained as free-standing films with very high surface area. Through control of the reaction conditions the pore-size distribution may be varied from predominantly microporous to predominantly mesoporous materials. These are the first materials to use cellulose as both the structural template and carbon source for a mesoporous carbon material. These are also the first carbon materials to combine mesoporosity with long-range chiral ordering. Possible applications for these materials include: charge storage devices (e.g. supercapacitors and anodes for Li-ion batteries), adsorbents, gas purifiers, light-weight nanocomposite materials, catalyst supports (e.g., for chiral transformations), gas storage, and as a hard-template to generate other materials, preferably with chiral structures.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. patent application Ser. No.13/076,469 filed Mar. 31, 2011, published as US 2011-0248214 on Oct. 13,2011 and the contents thereof are incorporated herein by reference.

TECHNICAL FIELD

This invention relates to a mesoporous carbon and a process for itspreparation.

In particular the present invention relates to a new material madepredominantly of carbon and having both a mesoporous structure andlong-range ordering (chiral nematic or nematic) that arises from theordering of a nanocrystalline cellulose (NCC) template.

BACKGROUND ART

Porous carbon materials are extensively used in many modern applicationsdue to their wide availability and excellent physical and chemicalproperties.¹ Some important examples include uses as catalyst supports,adsorbents for separation and gas storage, and in energy storage devices(e.g., batteries). The majority of commercially available porous carbonsare microporous (pores <2 nm) and are typically produced by thepyrolysis of organic precursors such as coal, wood, or polymers,followed by a physical or chemical activation step.² These materialshave been used commercially for many years and may be produced in bulkquantities at low cost. Several key drawbacks, however, have beenidentified for conventional microporous carbons, principally: (i) broadpore-size distributions, (ii) slow mass transport of molecules due tothe small pore sizes, (iii) low conductivity due to functionalizationincurred during activation, and (iv) collapse of the porous structureduring high-temperature treatments.¹ Recent development of newnanostructured carbon materials has the potential to address some ofthese issues and provide new opportunities for applications. Inparticular the incorporation of larger pores into carbonaceous materialscan be advantageous for a range of applications including the adsorptionof large molecules, chromatography, electrochemical double-layercapacitors, and lithium ion batteries.³⁻⁵

Template-synthesis of inorganic solids using the self-assembly oflyotropic liquid crystals offers access to materials with well-definedporous structures.⁷⁻¹⁶ Since it was described in 1992 by Beck et al.,liquid crystal templating has become a very important method todeveloping periodic materials with organization in the 1-100 nmdimension range. Mesoporous solids are typically formed from condensingan inorganic precursor (e.g., tetraethoxysilane) in the presence of aliquid crystalline template followed by the removal of the template.Although ionic surfactants were used in the original invention, diversemolecular (e.g., non-ionic surfactants) and polymeric substances havebeen used as templates. The materials obtained typically have periodicpores in the mesopore range of 2-50 nm in diameter that may be organizedinto hexagonal, cubic, or other periodic structures.

In 1999 it was reported that mesoporous silica could act as ahard-template for mesoporous carbon,¹⁷ thus providing the first exampleof a highly ordered mesoporous carbon material. Hard-templating ofcarbon typically involves the impregnation of a mesoporous“hard-template” with a suitable carbon source and acid catalyst followedby carbonization and selective removal of the template.

FIG. 1 shows a scheme illustrating the way that carbon materials havebeen previously prepared using hard-templating. In the first step, asurfactant (molecule or polymer) assembles into a liquid crystallinephase (step a), and a silica precursor (and often a catalyst) is addedin step b to give a mesostructured silica-surfactant composite, which isisolated. The sacrificial template is then removed by pyrolysis orsolvent extraction (step c), to give a mesoporous silica host.Subsequently, the mesoporous silica host is impregnated with a carbonsource (e.g., sugar) as shown in step d then pyrolyzed under inertatmosphere as shown in step e to give a mesoporous silica host that ispartially loaded with carbon. Besides the high number of steps needed inthis route, one of the drawbacks is the difficulty in fully loading themesoporous host. Consequently, steps d and e are often repeated severaltimes. Once the material is sufficiently loaded (as shown in step f),the silica host is removed with a procedure known to dissolve silica,often using aqueous or alcoholic hydroxide salts (e.g., NaOH, KOH,NH₄OH) or hydrogen fluoride (HF) (step g) to give the mesoporous carbon.

In this case the hard-template essentially acts as a mould whose porestructure remains unchanged during the impregnation and carbonizationsteps. The hard-templates that have been explored are most commonlyblock-copolymer or surfactant templated periodic mesoporous silicas,such as SBA-15 and MCM-48. Using the approach shown in FIG. 1 anddescribed above, numerous mesoporous carbon materials have beensynthesized with various ordered pore structures (e.g., hexagonal andcubic).¹⁸⁻²⁰ Several limitations to this approach exist including (i)the sacrificial use of expensive block-copolymers or surfactants, (ii)the necessity for multiple loading steps, and (iii) the difficulty ofsynthesizing films and monoliths.¹

Cellulose is the major constituent of wood and plant cell walls and isthe most abundant biomaterial on the planet. Cellulose is therefore anextremely important resource for the development of sustainabletechnologies. The rigid polymeric structure of native cellulose givesrise to excellent mechanical properties but has prevented its use forthe hard-templating synthesis of mesoporous carbons as described above.Despite this, the synthesis of mesoporous carbon directly from cellulosecould provide a cheap, renewable route to carbon materials. In nature,cellulose exists as the main constituent in the cell wall material ofplant and wood fibres which may be regarded as concentric compositetubes whose diameters are on the order of several microns. Stablesuspensions of cellulose nanocrystals can be obtained through sulfuricacid hydrolysis of bulk cellulosic material.²¹ In water, suspensions ofnanocrystalline cellulose (NCC) organize into a chiral nematic phasethat can be preserved upon air-drying resulting in chiral nematicfilms.^(22,23) The high-surface area, unique structural, andself-assembly properties of NCC make it a very interesting potentialtemplate for porous materials.

The chiral nematic (or cholesteric) liquid crystalline phase, wheremesogens organize into a helical assembly, was first observed forcholesteryl derivatives but is now known to exist for a variety ofmolecules and polymers. The helical organization of a chiral nematicliquid crystal (LC) results in iridescence when the helical pitch is onthe order of the wavelength of visible light due to the angle-dependentselective reflection of circularly polarized light. For this reason,chiral nematic LCs have been extensively studied for their photonicproperties and used for applications such as in polarizing mirrors,reflective displays, and lasers.²⁴⁻²⁶ Incorporation of chiral nematicorganization into solid-state structures could provide materials withnovel properties. We have recently reported that this may be achieved byusing NCC as a lyotropic chiral nematic template.^(27,28) Various silicaprecursors may be added to aqueous suspensions of NCC without disruptingthe chiral nematic phase and, following slow evaporation, NCC-silicacomposite films are obtained. We have shown that by removing the NCC,these composite films can be used to produce chiral nematic mesoporoussilica that reflects circularly polarized light. Furthermore, theNCC-containing composite films have the potential to be converted tochiral nematic mesoporous carbon by directly using cellulose as thecarbon source. This would provide a simple procedure for producingmesoporous carbon from cellulose that could be used for the applicationsmentioned above. The chirality of these materials could also result innovel properties that have previously not been associated withmesoporous carbon materials.

DISCLOSURE OF THE INVENTION

This invention seeks to provide a process for producing a mesoporouscarbon material.

This invention also seeks to provide a mesoporous carbon material.

In one aspect of the invention there is provided a process for producinga mesoporous carbon material comprising:

i) carbonising nanocrystalline cellulose (NCC) in an inorganic matrix,andii) removing the inorganic matrix from the carbonised NCC.

In another aspect of the invention there is provided a mesoporous carbonhaving a chiral nematic organization.

In still another aspect of the invention there is provided a mesoporouscarbon wherein the carbon is a carbonized cellulose, especially apyrolysed NCC.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Schematic illustrating a prior art method for making mesoporouscarbon using a mesoporous silica template.

FIG. 2: Schematic illustrating the method of the invention for makingmesoporous carbon using nanocrystalline cellulose as a template.

FIG. 3: IR spectrum of NCC-silica composite sample from preparation 2.

FIG. 4: IR spectrum of carbon-silica composite sample from preparation2.

FIG. 5: PXRD of NCC-silica composite sample from preparation 2.

FIG. 6: PXRD of carbon sample from preparation 2.

FIG. 7: TGA (air, 20° C./min) of NCC-silica composite sample frompreparation 2.

FIG. 8: TGA (air, 20° C./min) of carbon-silica composite sample frompreparation 2.

FIG. 9: IR spectrum of carbon sample from preparation 2.

FIG. 10: IR spectrum of carbon sample from preparation 4

FIG. 11: TGA (air, 20° C./min) of carbon sample from preparation 2.

FIG. 12: N₂ adsorption/desorption isotherm of carbon sample frompreparation 1 in which plots for adsorption and desorption are shownwhich partially overlap.

FIG. 13: N₂ adsorption/desorption isotherm of carbon sample frompreparation 2 in which plots for plots for adsorption and desorption areshown which partially overlap.

FIG. 14: N₂ adsorption/desorption isotherm of carbon sample frompreparation 3 in which plots for plots for adsorption and desorption areshown which partially overlap.

FIG. 15: N₂ adsorption/desorption isotherm of carbon sample frompreparation 4 in which plots for plots for adsorption and desorption areshown which partially overlap.

FIG. 16: N₂ adsorption/desorption isotherm of carbon sample frompreparation 5 in which plots for plots for adsorption and desorption areshown which overlap.

FIG. 17: BJH pore size distribution (adsorption) of carbon sample frompreparation 1.

FIG. 18: BJH pore size distribution (adsorption) of carbon sample frompreparation 2.

FIG. 19: BJH pore size distribution (adsorption) of carbon sample frompreparation 3.

FIG. 20: BJH pore size distribution (adsorption) of carbon sample frompreparation 4.

FIG. 21: BJH pore size distribution (adsorption) of carbon sample frompreparation 5.

FIG. 22: TEM image of carbon sample from preparation 2.

FIG. 23: SEM image of carbon sample from preparation 4.

FIG. 24: SEM image of carbon sample from preparation 2.

FIG. 25: SEM image of carbon sample from preparation 1.

FIG. 26: SEM image of carbon sample from preparation 5.

FIG. 27: CD spectrum of silica from preparation 6.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides a method for preparing mesoporous carbonaceousmaterials, especially chiral, mesoporous carbonaceous materials. Themethod is substantially simpler than the methods previously used forhard-templating mesoporous carbon, and incorporates new properties inthe resulting carbon-based material (chirality and the ability to formfree-standing films), in which said properties may be useful for avariety of applications. The free-standing films of mesoporous carbonproduced by the method of the invention typically have a surface areagreater than 1000 m²/g which is markedly higher than prior films ofmesoporous carbon produced by other methods (usually 600-800 m²/g).

In one embodiment the new method produces mesoporous carbon materialsthat have chiral nematic structure. This method takes advantage of thehigh surface area and self-assembly properties of nanocrystallinecellulose (NCC) as well as its utility as a carbon precursor. When asuitable precursor to silica (e.g., tetraethoxysilane, TEOS, ortetramethoxysilane, TMOS) is hydrolyzed in the presence of NCC a film isobtained after drying in which the NCC suspension has self-assembledinto a chiral nematic structure. The films obtained are compositestructures of cellulose nanocrystals embedded in a silica matrix. Uponpyrolysis under inert atmosphere (which can be any gas that does notpromote oxidation of the carbon, including nitrogen, helium, neon,argon, and other commonly used inert gases, or under vacuum) to convertthe NCC template to carbon at an elevated temperature, suitably 500° C.to 2000° C., especially 500° C. to 1000° C., and typically at 900° C.under nitrogen; and subsequent removal of the silica matrix, typicallyusing NaOH or a similar strong base (e.g., KOH, NH₄OH) in water, alcohol(e.g., methanol, ethanol), or a mixture thereof, although HF may also beemployed, a mesoporous carbon material is obtained as a powder or as afilm, depending on the morphology of the starting composite. Typicallythe removal of the silica matrix may be by heating in an aqueous alkali,for example sodium hydroxide, at a temperature of 20° C. to 100° C.,especially 70° C. to 100° C.

Any process for removing the matrix may be employed provided it does notdeleteriously affect the remaining carbonized NCC which is the desiredend product.

Nitrogen adsorption measurements indicate that the carbon materials aremesoporous and have large surface areas. These new mesoporous carbonmaterials have chiral nematic structures that may be directly observedby electron microscopy. These novel materials are attractive for manypractical applications, including catalyst supports (for chiral orachiral transformations), supercapacitors, batteries, fuel cells,adsorbents, lightweight reinforcement materials, components ofcomposites, and as templates for other chiral nanomaterials.

In a particular embodiment of this invention, a silica precursor ispolymerized in the presence of NCC to create materials with cellulosenanocrystallites organized in the silica matrix. After pyrolysis of thecellulose at elevated temperature under inert atmosphere and removal ofthe silica, a mesoporous carbon material is obtained.

FIG. 2 shows the schematic route to the preparation of the chiral,mesoporous carbon materials. In step (a), a silica precursor ishydrolyzed in a solution of NCC and the mixture is slowly dried, givingan NCC-silica composite material with chiral nematic order. In step (b),the composite material is pyrolyzed under inert atmosphere to give acarbon/silica composite material. Finally, in step (c), the silica isremoved (e.g., using aqueous or alcoholic NaOH or another strong base)to give mesoporous carbon with chiral nematic order.

The full synthesis (step (a) of FIG. 2) and characterization ofNCC-silica composite films has been described in U.S. patent applicationSer. No. 13/076,469 filed Mar. 31, 2011, the contents of which areincorporated herein by reference. The samples described herein wereprepared with different ratios of silica precursor to NCC (Preparations1-3). An additional control sample was prepared from pure NCC(Preparation 5). Carbonization was achieved by pyrolysis of thecomposite films at 900° C. (with the exception of Preparation 4, whichwas pyrolyzed at 600° C.) for 6 h under nitrogen. This results in shinyblack films that generally still display some iridescence. The filmswere characterized by infrared (IR) spectroscopy (FIGS. 3-4) and powderX-ray diffraction (PXRD) (FIGS. 5-6) before and after pyrolysis, whichclearly demonstrates the conversion of cellulose to amorphous carbon.The carbon yields were determined by thermogravimetric analysis (TGA)before and after carbonization and are found to be as high as 30 wt %for Preparation 2 (FIGS. 7-8). These carbon yields are much higher thanthe typically reported yields of 10-15 wt % for carbonization ofcellulose under N₂.^(29,30) It has been well-established that theaddition of sulfuric acid prior to pyrolysis can increase the carbonyield when cellulose or glucose is used as the carbon precursor.^(31,17)The surface of NCC utilized in the invention is already functionalizedwith sulfate groups and it is believed that this as well as theencapsulation of the NCC in the silica helps to obtain a high yieldwithout the need for a separate sulfuric acid impregnation step. Removalof the silica from the composite materials was achieved by heating thesamples to 85-90° C. in a 2M aqueous NaOH solution. After rinsing thefilms with water and drying, the removal of the silica was confirmed byIR spectroscopy (FIGS. 9-10) and TGA (FIG. 11), which show the loss ofthe Si—O peak and a residual mass of 3 wt % after heating under air to900° C.

Nitrogen adsorption was used to study the porosity of the differentcarbon samples. Type IV adsorption isotherms with hysteresis loops,indicative of mesoporous materials, are observed for the carbon obtainedusing Preparations 1-4 (FIGS. 12-15). The control sample prepared frompure NCC (Preparation 5) gives a type I isotherm indicative of a purelymicroporous material (FIG. 16). The isotherm shapes, BET surface areas,and pore volumes show a strong dependence on the amount of silica usedin the preparation. Preparation 2, which uses an intermediate amount ofsilica precursor, gives mesoporous carbon with the highest BET surfacearea (1465 m²/g). In comparison, carbon samples prepared with lesssilica (Preparation 1) or more silica (Preparation 3) both have smallerBET surface areas (907 m²/g and 1230 m²/g respectively). The t-plotanalysis of these samples shows a significant micropore contribution tothe overall surface area (˜10% of the total surface area) whereasPreparation 2 gives a material with essentially no microporecontribution. An additional sample was prepared using the same procedureas Preparation 2 except that pyrolysis was carried out at 600° C.(Preparation 4). The N₂ adsorption/desorption isotherms for Preparations2 and 4 (FIG. 15) are nearly identical showing that mesoporous carbonmaterials may be obtained by our method using different pyrolysistemperatures. The IR spectrum for mesoporous carbon prepared at 600° C.indicates the presence of some residual functional groups (FIG. 10).This demonstrates that different synthetic temperatures may be usefulfor fine-tuning the surface properties of the mesoporous carbon.

The BJH pore size distributions derived from the adsorption branch ofthe isotherms for Preparations 1-5 are shown in FIGS. 17-21. The poresize distribution calculated for Preparation 1 shows a sharp rise inpore volume beginning at ˜4 nm (FIG. 17) with no peak observed before 2nm. Carbon prepared from Preparation 2 on the other hand shows a fairlybroad peak at 2.8 nm with essentially no pore volume past 6 nm (FIG.18). Cylindrical mesopores for this sample were also visualized bytransmission electron microscopy (TEM, FIG. 22). Preparation 3 yieldscarbon that has a very broad pore distribution with pore volumebeginning around 11 nm and gradually increasing to a plateau at 2.5 nm(FIG. 19). As expected, the microporous carbon from Preparation 5 showsvery little pore volume before 2 nm (FIG. 21, note the scale on they-axis is an order of magnitude smaller than for FIG. 17-20). Theseresults further illustrate the importance of the silica in thepreparation of the mesoporous carbon samples. Varying the relativeamounts of NCC and silica shows that there is an ideal window forobtaining a mesoporous product; it is clear that an adequate silicawall-thickness is required for mesopore formation. On the other hand,when too much silica is used the pore size distribution is very broadand micropores begin to reappear. By way of example a suitable ratiobased on TMOS (tetramethoxysilane) or TEOS (tetraethoxysilane) as thesource of the inorganic matrix would be 4-16.5 mmol TMOS or TEOS /g NCCand preferably about 9 mmol TMOS or TEOS /g NCC in terms of max surfacearea and mesoporosity. We postulate that some carbon bridges arerequired to form between the silica walls during pyrolysis in order forthe structure to be retained after the removal of silica. When thesilica walls are too thick, these bridges are formed less effectively.Overall, these results clearly show that mesoporous carbon may beobtained using our new approach. Through a simple variation in thesynthesis, namely the relative amounts of silica precursor and NCC thatare used, the ratio of mesopores to micropores in the materials may bealtered. Further optimization of these conditions within the idealsynthetic window should allow for further fine-tuning of the porosity ofthe mesoporous carbon materials.

Scanning electron microscopy (SEM) provides evidence of the replicationof chiral nematic organization in the mesoporous carbon films fromPreparations 2, 3, and 4. Perpendicular to the surface of the film, alayered structure is observed with a repeating distance of severalhundred nanometers that arises from the helical pitch of the chiralnematic phase (FIG. 23). At higher magnification a well-defined twistingrod-like morphology is resolved (FIG. 24). Throughout the entire sample,this twisting appears to occur in a counter-clockwise direction whenmoving away from the viewer, which corresponds to a left-handed helicalorganization. Preparations 2-4, which correspond to the most mesoporoussamples, also show the best retention of chiral nematic organization. Asa comparison, a much less well-defined structure was observed forPreparation 1 (FIG. 25). The control sample (Preparation 5) appears muchmore disordered (FIG. 26) and generally does not retain the chiralnematic structure of the original NCC films. The silica clearly has aprotective effect during pyrolysis that allows for the chiral nematicstructure to remain intact in conjunction with the templation ofwell-defined mesopores.

To further confirm the chirality of the mesoporous carbon anddemonstrate its utility as a template for other chiral materials,mesoporous carbon from preparation 2 was used to template silica.Repeated loading and condensation of TEOS within the pores of the filmsfollowed by removal of the carbon results in transparent silica. Thesilica is birefringent by polarized optical microscopy (POM) with atexture similar to that observed in pure NCC films with chiral nematicorganization. Circular dichroism shows a strong signal with positiveellipticity resulting from chiral reflection at 327 nm (FIG. 27). Thisexperiment further confirms that the carbonaceous material fromPreparation 2 has a chiral structure, and that it can be transferred toother materials.

The materials prepared herein always have an organization that shows apositive ellipticity by CD (left-handed organization). The otherorganization (right-handed) is not known, but if it could be discovered,then this method should be applied to make the enantiomeric structure.While the examples herein are of materials from silica, other inorganicand metal-organic structures (e.g., based on organosilanes) and whichmaintain their integrity under condition for carbonizing the NCC andwhich can thereafter be removed, can also be employed.

Mesoporous carbon without chiral nematic organization may also beobtained from NCC by using a procedure identical to Preparation 2 withone modification, that modification being that the pH of the NCCsuspension is adjusted to a pH where the chiral nematic ordering isdisrupted during the synthesis of the composite (Preparation 7). Whenthe pH of the NCC suspension was adjusted to 2.0, transparent NCC-silicacomposite films were obtained. The films were determined to be achiralthrough UV-Vis-NIR spectroscopy, which did not reveal any reflection dueto the chiral nematic organization within the range of 300-3000 nm. SEMimages also did not reveal any chiral nematic organization within thefilms but instead indicate that the films possess nematic ordering. POMimages further suggest that the organization of NCC within the achiralcomposite films is most likely nematic. After pyrolysis under N₂ and theremoval of silica, free-standing carbon films were obtained. N₂adsorption experiments demonstrate that the achiral carbon films aremesoporous with similar adsorption characteristics compared to themesoporous carbon obtained from Preparation 2. SEM images of themesoporous carbon do not reveal any chiral nematic organization.Mesoporous carbon may therefore be synthesized from NCC with both chiraland achiral structures.

Examples

In the Examples, sonication was applied to ensure that the NCC particleswere dispersed. The sonicator was a standard laboratory model (2 A, 120V) available from VWR (Aquasonic model 50T). A sonication time of 10-15minutes was typically applied prior to addition of thesilicon-containing compound.

Preparation 1. Synthesis of NCC/Silica Composite:

1.00 mL of TEOS is added to 30.0 mL of a freshly sonicated 3.5% aqueousNCC suspension. The mixture is stirred at 60° C. until a homogeneousmixture is obtained (˜4 h), indicating complete hydrolysis of the TEOS.The mixture is poured into polystyrene Petri dishes and after slowevaporation at room temperature slightly red films are obtained.

Pyrolysis:

Under flowing nitrogen, 1.00 g of the NCC/silica composite films isheated at a rate of 2° C./min to 100° C. for 2 h, then heated at 2°C./min to 900° C. for 6 h, and finally cooled to room temperature at 4°C./min. After slowly cooling to room temperature 372 mg of free-standingblack films are recovered. The IR spectrum of the sample confirms theconversion of NCC to carbon. The mass yield of carbon calculated fromTGA is 28.1%.

Silica Etching:

300 mg of the carbon/silica composite films are placed in a beakercontaining 200 mL of 2M aqueous NaOH solution and heated to 90° C. for 4h. The films are then recovered by filtration and rinsed with copiousamounts of water. After air drying 152 mg of carbon films are recovered.The IR spectrum of the sample confirms the removal of silica and TGAgives a 3.8 wt % residue after heating to 900° C. under air. Nitrogenadsorption measurements show a BET surface area of 907 m²/g (microporearea from t-plot=103 m²/g) and a pore volume of 0.56 cm³/g (FIG. 12).SEM images reveal that the chiral nematic structure is poorly retainedin the carbon product (FIG. 25).

Preparation 2. Synthesis of NCC/Silica Composite:

1.40 mL of TMOS is added to 30.0 mL of a freshly sonicated 3.5% aqueousNCC suspension. The mixture is stirred at room temperature until ahomogeneous mixture is obtained (˜1 h), indicating complete hydrolysisof the TMOS. The mixture is poured into polystyrene Petri dishes andafter slow evaporation at room temperature colourless films areobtained.

Pyrolysis:

Under flowing nitrogen, 1.00 g of the NCC/silica composite films isheated at a rate of 2° C./min to 100° C. for 2 h, then heated at 2°C./min to 900° C. for 6 h, and finally cooled to room temperature at 4°C./min. After slowly cooling to room temperature 505 mg of free-standingblack films are recovered. The IR spectrum of the sample (FIG. 4) andPXRD (FIG. 6) confirms the conversion of NCC to carbon. The mass yieldof carbon calculated from TGA is 29.6%

Silica Etching:

500 mg of the carbon/silica composite films are placed in a beakercontaining 200 mL of 2M aqueous NaOH solution and heated to 90° C. for 4h. The films are then recovered by filtration and rinsed with copiousamounts of water. After air drying 175 mg of carbon films are recovered.The IR spectrum of the sample confirms the removal of silica (FIG. 9)and TGA gives a 3.2 wt % residue after heating to 900° C. under air(FIG. 11). Nitrogen adsorption measurements show a BET surface area of1465 m²/g (micropore area from t-plot=11 m²/g) and a pore volume of 1.22cm³/g (FIG. 13). TEM images show long locally aligned pores (FIG. 22).SEM images reveal a structure consistent with chiral nematicorganization (FIG. 24).

Preparation 3. Synthesis of NCC/Silica Composite:

2.50 mL of TMOS is added to 30.0 mL of a freshly sonicated 3.5% aqueousNCC suspension. The mixture is stirred at room temperature until ahomogeneous mixture is obtained (˜1 h), indicating complete hydrolysisof the TMOS. The mixture is poured into polystyrene Petri dishes andafter slow evaporation at room temperature colorless films are obtained.

Pyrolysis:

Under flowing nitrogen, 1.00 g of the NCC/silica composite films areheated at a rate of 2° C./min to 100° C. for 2 h, then heated at 2°C./min to 900° C. for 6 h, and finally cooled to room temperature at 4°C./min. After slowly cooling to room temperature 490 mg of free-standingblack films are recovered. The IR spectrum of the sample confirms theconversion of NCC to carbon. The mass yield of carbon calculated fromTGA is 19.1%

Silica Etching:

450 mg of the carbon/silica composite films are placed in a beakercontaining 200 mL of 2M aqueous NaOH solution and heated to 90° C. for 4h. The films are then recovered by filtration and rinsed with copiousamounts of water. After air drying 82 mg of carbon films are recovered.The IR spectrum of the sample confirms the removal of silica. Nitrogenadsorption measurements show a BET surface area of 1230 m²/g (microporearea from t-plot=128 m²/g) and a pore volume of 0.96 cm³/g (FIG. 14).SEM images reveal a structure consistent with chiral nematicorganization.

Preparation 4. Synthesis of NCC/Silica Composite:

2.00 mL of TMOS is added to 50.0 mL of a freshly sonicated 3.0% aqueousNCC suspension. The mixture is stirred at room temperature until ahomogeneous mixture is obtained (˜1 h), indicating complete hydrolysisof the TMOS. The mixture is poured into polystyrene Petri dishes andafter slow evaporation at room temperature colorless films are obtained.

Pyrolysis:

Under flowing nitrogen, 1.50 g of the NCC/silica composite films areheated at a rate of 2° C./min to 100° C. for 2 h, then heated at 2°C./min to 600° C. for 6 h, and finally cooled to room temperature at 4°C./min. After slowly cooling to room temperature 766 mg of free-standingblack films are recovered. The IR spectrum of the sample confirms theconversion of NCC to carbon, although some functional groups stillremain due to the lower pyrolysis temperature (FIG. 10). The mass yieldof carbon calculated from TGA is 27.9%

Silica Etching:

500 mg of the carbon/silica composite films are placed in a beakercontaining 200 mL of 2M aqueous NaOH solution and heated to 90° C. for 4h. The films are then recovered by filtration and rinsed with copiousamounts of water. After air drying 180 mg of carbon films are recovered.The IR spectrum of the sample confirms the removal of silica. Nitrogenadsorption measurements show a BET surface area of 1330 m²/g (microporearea from t-plot=38 m²/g) and a pore volume of 1.12 cm³/g (FIG. 15). SEMimages reveal a structure consistent with chiral nematic organization(FIG. 23).

Preparation 5. Synthesis of Control Sample:

NCC films are prepared by slow evaporation at room temperature inpolystyrene Petri dishes. Under flowing nitrogen, 1.00 g of theNCC/silica composite films are heated at a rate of 2° C./min to 100° C.for 2 h, then heated at 2° C./min to 900° C. for 6 h, and finally cooledto room temperature at 4° C./min. After slowly cooling to roomtemperature 205 mg of free-standing black films (mass yield=20.1%) arerecovered. The IR spectrum of the sample confirms the conversion of NCCto carbon. Nitrogen adsorption measurements show a BET surface area of674 m²/g (micropore area from t-plot=574 m²/g) and a pore volume of 0.40cm³/g (FIG. 16). SEM images indicate that the chiral nematic structureof the NCC has been lost during pyrolysis (FIG. 26).

Preparation 6.

Replication of Silica from Mesoporous Carbon:

67 μL of TEOS and 10 μL of 0.1 M HCl solution are mixed together andadded dropwise to 52 mg of mesoporous carbon films from preparation 1 ina glass vial. After brief agitation, the vial is placed in an oven at40° C. for 1 h followed by 80° C. for 1 h. The loading procedure isrepeated 10 times.

Pyrolysis:

After the final loading, the films are placed in a tube furnace underflowing N₂ and heated at a rate of 2° C./min to 600° C. for 6 h. Thepyrolysis is then repeated under flowing air to remove the carbonresulting in transparent silica films (m=65 mg). Circular dichroism ofthe silica films showed a chiral reflection peak at 327 nm (FIG. 27).

Preparation 7. Synthesis of Achiral NCC/Silica Composite:

The pH of a 3.5 wt. % NCC suspension is adjusted to pH 2.0 through thedropwise addition of 1 M hydrochloric acid. 1.40 mL of TMOS is added to30.0 mL of a freshly sonicated 3.5% aqueous NCC suspension at pH 2.0.The mixture is stirred at room temperature until a homogeneous mixtureis obtained (˜1 h), indicating complete hydrolysis of the TMOS. Themixture is poured into polystyrene Petri dishes and after slowevaporation at room temperature colourless films are obtained.

Pyrolysis:

Under flowing nitrogen, 1.28 g of the NCC/silica composite films isheated at a rate of 2° C./min to 100° C. for 2 h, then heated at 2°C./min to 900° C. for 6 h, and finally cooled to room temperature at 4°C./min. After slowly cooling to room temperature 557 mg of free-standingblack films are recovered. The IR spectrum of the sample and PXRDconfirms the conversion of NCC to carbon.

Silica Etching:

500 mg of the carbon/silica composite films are placed in a beakercontaining 200 mL of 2M aqueous NaOH solution and heated to 90° C. for 4h. The films are then recovered by filtration and rinsed with copiousamounts of water. After air drying 160 mg of carbon films are recovered.The IR spectrum of the sample confirms the removal of silica. Nitrogenadsorption measurements show a BET surface area of 1224 m²/g (microporearea from t-plot=74 m²/g) and a pore volume of 1.03 cm³/g (FIG. 13). SEMimages reveal the absence of chiral nematic organization in themesoporous carbon.

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1. A process for producing a mesoporous carbon material comprising: i)carbonising nanocrystalline cellulose (NCC) in an inorganic matrix, andii) removing the inorganic matrix from the carbonised NCC.
 2. A processaccording to claim 1, wherein said carbonising comprises pyrolysis ofthe NCC under an inert atmosphere at an elevated temperature.
 3. Aprocess according to claim 2, wherein said inert atmosphere is nitrogenand said elevated temperature is 500° C. to 2000° C.
 4. A processaccording to claim 1, wherein said inorganic matrix is silica and ii)comprises heating in an aqueous alkali.
 5. A process according to claim4, wherein said alkali is sodium hydroxide and said heating is at 20° C.to 100° C.
 6. A process according to claim 1, wherein said NCC in theinorganic matrix comprises said NCC in a chiral nematic arrangement andi) and ii) are carried out with maintenance of the chiral nematicarrangement of the NCC in the carbonised NCC.
 7. A process according toclaim 1, further comprising: iii) recovering said carbonised NCC as afilm.
 8. A process according to claim 1, further comprising: iii)recovering said carbonised NCC as a powder.
 9. A mesoporous carbonhaving a chiral nematic organization.
 10. The mesoporous carbonaccording to claim 9, wherein said carbon is carbonised NCC.
 11. Themesoporous carbon according to claim 9, wherein said carbon is pyrolysedNCC.
 12. The mesoporous carbon according to claim 10, in the form of afilm.
 13. The mesoporous carbon according to according to claim 10, inthe form of a powder.
 14. The mesoporous carbon according to claim 12,wherein said film has a surface area greater than 1000 m2/g.
 15. Aprocess according to claim 3, wherein said inorganic matrix is silicaand ii) comprises heating in an aqueous alkali.
 16. A process accordingto claim 15, wherein said alkali is sodium hydroxide and said heating isat 20° C. to 100° C.
 17. A process according to claim 15, wherein saidNCC in the inorganic matrix comprises said NCC in a chiral nematicarrangement and i) and ii) are carried out with maintenance of thechiral nematic arrangement of the NCC in the carbonised NCC.
 18. Aprocess according to claim 16, wherein said NCC in the inorganic matrixcomprises said NCC in a chiral nematic arrangement and i) and ii) arecarried out with maintenance of the chiral nematic arrangement of theNCC in the carbonised NCC.
 19. A process according to claim 17, furthercomprising: iii) recovering said carbonised NCC as a film.
 20. A processaccording to claim 18, further comprising: iii) recovering saidcarbonised NCC as a powder.